Gas operated fireplaces with sealed combustion chambers have been in use for many years. Such fireplaces may be installed in a pre-existing wood burning fireplace enclosure or in a specially configured alcove anywhere in a room. Such fireplaces typically include a firebox containing the combustion chamber and an outer casing surrounding the firebox, with a space therebetween. Located inside the firebox is a gas burner and material which, when heated, simulates a wood or coal fire. For example, artificial logs are often used to simulate wood logs. The casing has an open front larger than the firebox to permit air to enter and exit the space between the firebox and casing. The space between the firebox and outer casing is often referred to as a "room air wipe", which allows air circulation around the firebox. Typically, room air enters the air wipe below the firebox, circulates around the firebox and exits the air wipe back into the room above the firebox, thereby heating the room and cooling the firebox. Typically, louvers are located in the air wipe, both above and below the firebox. A viewing panel, or window, is positioned on the front of the firebox to allow viewing of the simulated fire and to seal the firebox to achieve a sealed combustion system.
The use of a balanced co-axial flue is well known in the art. Co-axial flues are commonly available in rigid or flexible configurations, and are used for both vertical and horizontal venting configurations. The firebox has a stub flue, which mates with the inner co-axial duct through which exhaust gases from the firebox are conveyed to external ambient. The inner co-axial duct is fastened to the stub flue by known means, such as a gear clamp or crimping. An outer fitting on the casing surrounds the stub flue to leave an annular opening to admit intake air for combustion. It mates with the outer portion of a standard co-axial flue, which is similarly held in place by a gear clamp or crimping. A sealed manifold assembly carries the intake air from the annular opening to the firebox for combustion. While exhaust gases flow out the inner duct, their place is taken by intake air which flows inward along the outer, annular passage of the balanced flue. Counterflow heat transfer from the exhaust gases thereby pre-heats the incoming air.
Considerable effort has been devoted to making the gas fire and artificial logs look like a real wood fire. Real wood fires have predominantly yellow flames, which are typically associated with lower flame temperatures and higher levels of carbon monoxide emissions. The challenge is to provide an attractive yellow flame pattern and still meet applicable emission standards. Because complete combustion of the gas usually results in a blue flame, rather than a yellow flame normally associated with a real wood fire, it has been difficult to achieve both complete combustion of the gas and the visual appearance of a real wood fire. Various techniques have been used, including flame deflectors and chemical additives, in order to achieve a yellow flame appearance with complete combustion of the gas. Glowing ember strips, or emberizing materials, have been used to simulate beds of glowing coals under or in front of artificial fires. These strips often serve an additional cosmetic purpose in hiding the gas burner element. The glowing appearance of a real wood fire is difficult to achieve. It depends on the choice of artificial log material, which may be coated aluminum, solid ceramic, concrete, soft ceramic, or other material. It also depends on the geometry of the burner ports, the orientation of the burner relative to the artificial logs, the extent to which the flames impinge on the artificial logs, and the orientation of the artificial logs relative to each other and relative to any ember strips or emberizing materials.
Construction of existing prior art log fireplaces illustrates several problems. Almost all fireplaces now use a room air wipe. Many fireplaces use balanced flues. A recurring difficulty is how to carry the intake air from the balanced flue to the firebox, since it must traverse the air wipe in some way. There have been many variations. For example, units such as those described in U.S. Pat. Nos. 4,793,322 to Shimek, 4,909,227 to Rieger, and 5,267,552 to Squires, et at., all show configurations of rectilinear ductwork. Typically, sheet metal is folded to form rectilinear passageways. These folded sheet metal ducts are then incorporated in the structure to mate with the fireplace casing, or the firebox, or both.
Not only has the location of the intake ductwork been problematic, but fabrication of the firebox and casing enclosure has been complicated. In a balanced flue system, combustion air ducts, whether for intake or exhaust, must be sealed. Sealing is traditionally done by spot welding the seams of the ductwork and partitions within the units and then covering the seam with a sealant such as silicone. Welding the firebox and casing creates several problems. First, it is commonly associated with unitary fireplace construction. Unitary construction yields a heavy, cumbersome fireplace that usually cannot easily be repaired or replaced. Access to components is difficult once the unit is assembled. Second, it is difficult to maintain consistent quality along the welded seams. The sheet metal panels tend to warp and each successive weld makes it more difficult to maintain a fixed tolerance on the subsequent welds, thereby resulting in lower quality products in general. Third, the warpage in the panels and the residual stresses along the welded joints makes the fireplaces noisy. Heating and cooling cause the structure to flex and undesirable noises are emitted during flexure. Fourth, welding itself is also associated with a host of health and safety problems. Therefore, there has been a long-felt need both to simplify the intake air arrangement of sealed combustion fireplaces and to reduce or eliminate the welding required in their fabrication.
Yet another problem involves servicing the fireplace components. Typically, the entire fireplace assembly must be removed for servicing, which requires a service technician to cut into the room wall in order to remove the fireplace assembly. It is also difficult to obtain access to components, such as the burner or gas control valve. A related problem is that once an entire fireplace assembly has been installed during initial construction of a building it is susceptible to damage during subsequent stages of construction. Alternatively, in retrofit installations, a portion of a room wall must be removed to provide an alcove for installation of the fireplace assembly. Particularly during new construction, the fireplace assembly is susceptible to theft and damage. Still another problem associated with prior art artificial log fireplaces is that the alcove in which the fireplace assembly is installed must have sufficient space to accommodate the exhaust flue. The exhaust flue may be either vertical (i.e., emanating from a top panel of the fireplace assembly) or horizontal (i.e., emanating from a rear panel of the fireplace assembly). It is known in the art to provide a "universal" flue, which can be configured for either vertical or horizontal exhaust. However, the alcove must be made sufficiently large to accommodate a bend in the exhaust flue to achieve the desired vertical or horizontal orientation. It is known in the art to provide a top panel of the fireplace assembly having a 45.degree. downward slope. A 45.degree. sloped top permits either horizontal or vertical installation with the use of a rotatable 45.degree. elbow. However, the permissible minimum bend radius of a balanced co-axial flue is such that a greater than desired alcove depth may be required to accommodate a vertical 45.degree. arc of venting.
There is, therefore, a need for an improved gas operated fireplace assembly.